The present invention relates to a heat transfer recording material useful for recording images by means of heat transfer techniques using sublimable dyes (thermally migrating dyes) and, more specifically, to a heat transfer recording material capable of forming transferred images excellent in resistance to fingerprints and oils such as plasticizers, and having high density and resolution.
As a replacement to general printing techniques heretofore available, ink jet or heat transfer systems have been developed to give improved monochromatic or full-color images in a simple and fast manner. Of these systems, the most excellent is a so-called sublimation heat transfer system using sublimable dyes, which give full-color images having improved continuous gradation and are comparable to color photographs.
In general, a heat transfer sheet used with the aforesaid sublimation type of heat transfer system includes a substrate film such as a polyester film, which has a sublimable dye-containing dye layer on one side and a heat-resistant layer on the other side to prevent it from sticking to a thermal head.
The dye layer of such a heat transfer sheet is overlaid on an image-receiving sheet having an image-receiving layer formed of a polyester resin, etc., and heat is applied to the back side of the heat transfer sheet through a thermal head in an imagewise manner, so that the dye migrates from the dye layer onto the image-receiving sheet, forming the desired image.
Because the coloring material used is a dye, the aforesaid heat transfer system gives an image excelling in clearness, color reproducibility, etc. and being of a high quality comparable to that of a conventional photographic or printed image. One problem with this system, however, is that when fingers touch the image surface during handling, their lipid (fingerprints) is transferred onto the image, resulting in fading or discoloration of the image. Another problem is that when articles containing plasticizers such as plastic erasers or soft films, e.g., transparent files or articles containing other oils touch the image, the image-forming dye migrates onto such articles, so that they are contaminated or the image degrades considerably.
Although such problems may be solved by laminating a transparent film of a material such-as polyester on the image, it is so troublesome and costly that it may be used for special-purposes alone.